Vitamin D is a nutrient that the body needs to help it absorb calcium and phosphorus from food. Vitamin D also helps regulate normal muscle and immune function. People who are physically active tend to have lower levels of vitamin D but there isn’t much evidence that taking supplements can improve a person's ability to stay healthy. Most people in the U.S. get enough vitamin D from their diets. Many vitamin D supplements are not made from the form of vitamin D that the body can use. Some people are deficient in vitamin D but most people can get sufficient amounts from their diet.
Vitamin D deficiency has been associated with:
According to a review of studies, more than 90% of children and teenagers in some countries (United States, United Kingdom) have low blood levels of Vitamin D. Vitamin D is best absorbed when consumed in a supplement form or fatty foods rich in vitamins. The best foods for this are cod liver oil and dairy products such as milk and cheese.
The theory that sunlight exposure can prevent cancer and other chronic diseases has been popularized by media reports since the early 2000s. This "sunshine or vitamin D" theory has not been borne out by well-designed intervention studies. A 2008 critical review of the literature concluded that "on balance, it seems unlikely that sun exposure or vitamin D will prove to have major effects on prevention of common Western cancers, cardiovascular disease, or diabetes." However, results of randomized controlled trials continue to be published which may show a benefit of vitamin D supplementation in a variety of health conditions: bone density loss, high blood pressure, high blood glucose levels in non-diabetics without known diabetes mellitus, and multiple sclerosis. A 2014 Cochrane review found moderate evidence for the use of vitamin D supplements in reducing mortality in adults.
The optimal daily intake of vitamin D is unclear. Recommended dietary allowances are based on evidence that less than 10% of the population achieves adequate blood levels from sun exposure. The Institute of Medicine set the tolerable upper intake level (UL) for vitamin D at 4,000 IU per day for adults and 1,000 IU per day for children. As with most nutrients, there is no established recommended daily intake level.
In 2011, researchers at the National Health Research Institutes in Taiwan found that people with lower levels of vitamin D had significantly greater rates of mortality and heart disease in comparison to those with higher levels of vitamin D. Their results suggest that "a low serum concentration of 25-hydroxyvitamin D [25(OH)D] is associated with an increased risk for death. A 25(OH)D serum level below 30 ng/mL may be associated with a higher risk of death." Of the 13,000 participants in the study, only those with vitamin D levels below 22 nmol/L were at risk.
On June 11, 2012, researchers from Brigham and Women's Hospital and Harvard Medical School published a study in the journal "PLoS One" that suggests people with high blood levels of vitamin D may be less likely to develop heart disease. The research team decided to investigate whether or not vitamin D helps prevent heart disease by studying two groups of middle-aged men: those who had low blood levels of the nutrient and those who had high levels. The men were followed for four years. The researchers report that the men with high vitamin D levels were about 32 percent less likely to have suffered from heart attacks during the study period than those with low levels of vitamin D.
In 2012, a clinical trial was initiated in the UK to test the effects of adding vitamin D to existing heart disease treatment. The study is one of only a handful of clinical trials investigating vitamin D in heart disease. The trial will include more than 1,000 patients from the UK and Germany and is due to conclude in late 2013. Researchers at the Queen Mary University of London who initiated the study say that “caution should be adopted when considering supplementation with vitamin D for prevention or treatment of cardiovascular disease without supporting evidence for efficacy, particularly when current therapies are effective.”
Vitamin D is often used to treat rickets and osteomalacia in children. However, the Institute of Medicine of the National Academies has stated that "there is no evidence that vitamin D supplementation prevents fractures, falls or deaths related to falls" for adults. It also states there is no evidence that high doses of vitamin D are beneficial for adults with osteoporosis.
Vitamin D may be effective to treat certain types of cancer through its effects on cells known as immunocytes. Immunocytes are white blood cells that recognize and interact with cancerous cells. Vitamin D also encourages the body to defend against cancer. A study published in 2009 found that breast cancer patients who had low blood levels of vitamin D experienced greater relapse and death rates than those with high blood levels.
There is debate on the potential effects of vitamin D, as compared to calcium supplements, on cardiovascular disease and mortality. A 2013 study on elderly people reported that 1000 IU/day was associated with a lower rate of heart attack, stroke, and death compared to those given a placebo (38% vs. 12%). However, the same study reported that 2000 IU/day was actually associated with increased overall death (40% higher than placebo). A 2014 meta-analysis found no evidence that vitamin D was associated with a lower rate of cardiovascular disease or any cardiovascular events. A 2010 review criticized the quality of studies on both sides of the debate. The review examined ten randomized trials (4,289 participants) and found that neither vitamin D nor calcium supplementation reduced the risk for total cardiovascular events or cancer. In an accompanying editorial, two researchers writing on behalf of the European Society of Cardiology commented that all previous meta-analyses have been compromised by methodological flaws such as combining low dose supplements with dietary intakes, inappropriate statistical methods, and inclusion of nonrandomized patients.
The U.S. Institute of Medicine (IOM) has stated that the current evidence does not support a role for vitamin D supplements in reducing the risk of cardiovascular, cancer or autoimmune diseases. The IOM also stated that there was insufficient evidence to conclude whether vitamin D supplements had any beneficial effect on bone health.
In 2013, a review published in the Cochrane Database of Systematic Reviews found no evidence that vitamin D supplements reduce the risk of death from any cause. The review included data on 37,871 people from over 600 trials.
There has been some remarkable research into vitamin D's effects on inflammatory conditions such as diabetes and multiple sclerosis.
In 2003, a study in the UK found that the pain of arthritis was reduced by 50–70% in people taking vitamin D supplements. A 2007 review by the Arthritis Research Campaign in England found evidence that low vitamin D levels can exacerbate symptoms of arthritis, especially for inflamed joints like hands and wrists. The review also indicated a connection between low vitamin D levels and rheumatoid arthritis, which afflicts 1.3 million people in the UK.
However, a 2007 review (the VITAL study) found no evidence that vitamin D supplementation reduced the incidence of falls, fractures, or mortality in an elderly population. It also did not reduce the risk of developing cancer or heart disease.
Vitamin D is a hormone produced by most animal cells and is required for the maintenance of bone and normal cellular function. Vitamin D concentrations can be measured in either serum or plasma, with plasma typically being used in clinical practice. Vitamin D deficiency can lead to rickets in children and osteomalacia in adults. Symptoms may include muscle weakness, bone pain, and tenderness, as well as loss of height and flexibility due to reduced bone mineral density. Long-term deficiency in adults may also result in osteoporosis and an increased risk of fractures.
A 2010 review of several studies suggested that vitamin D deficiency is associated with an increased risk of colon cancer. The same review found no consistent association between vitamin D levels and breast cancer, although it noted that most research was done when few women took supplements containing vitamin D. A 2008 study by Hollis et al found no evidence that raising serum 25-hydroxyvitamin d concentrations affects the progression of prostate cancer.
Benefits of Vitamin D
There have been several studies that determined the benefits of vitamin D in the treatment and in the prevention of many diseases. One study conducted in Monterrey, Mexico; found that 49% of patients with multiple sclerosis who received vitamin D supplementation experienced significant improvement compared with a group of patients receiving only placebo treatment. The participants also experienced fewer relapses than those taking a placebo. Another study showed that vitamin D levels were low among patients with psoriasis, as well as among elderly people in nursing homes. The researchers concluded: “Low serum 25-hydroxyvitamin D concentrations may be associated with the pathogenesis of psoriasis and may represent a risk factor for the development and progression of this disease.” A 2006 study in the Journal of the American Medical Association found that people with depression were more likely to develop vitamin D deficiency if they were not taking any supplements.
Vitamin D is also essential for the regulation of calcium, phosphate, and magnesium in the body. It is involved in cell division, in the manufacture of a number of hormones and enzymes, promotes bone growth, and helps bones repair themselves after injury. Vitamin D deficiencies can cause a loss of muscle strength and bone density, making it important for older people as osteoporosis often affects them. Vitamin D supplements have been found to reduce the risk of falls in the elderly, who are also more susceptible to bone fractures.
In addition, vitamin D has beneficial effects on cells different from its role for bone and mineral metabolism. A series of observations in cell culture and animal models has led researchers to speculate that a wide variety of human diseases may be influenced by vitamin D, including cancer, chronic pain syndromes, multiple sclerosis, and cardiovascular diseases such as hypertension. At least two clinical trials are currently being conducted for cancer prevention.
Vitamin D has been shown to reduce overall cancer risk, particularly for colorectal cancer.
A study of 35,335 individuals in England and Scotland found that those with low vitamin D levels were almost twice as likely to develop cancer as those with high levels.
The link between low vitamin D and certain cancers is stronger in people with poor diets, those who do not get enough UV exposure or people whose skin is very dark.
Vitamin D also helps the body absorb calcium, which may lower the risk for colon cancer. Some studies show a link between calcium and vitamin D intake and a reduced risk for colorectal cancers in both men and women.
Vitamin D also plays a role in muscle function. Vitamin D supplements have been shown to improve muscle function in people with multiple sclerosis.
People experiencing a severe vitamin D deficiency may also be more susceptible to the common cold.
There is no significant evidence for vitamin D or vitamin D analogs (calciferol, ergocalciferol) improving health and functioning in older adults.
Some observational studies show an association between low vitamin D levels and lower cognitive performance, but it is unclear whether a relationship exists between low serum 25-hydroxyvitamin d levels and cognitive decline. Reviews by the United States Institute of Medicine, Health Canada, the National Research Council of Canada have found that there is little evidence to confirm that vitamin D supplementation reduces falls or fractures among individuals aged 60 or older.
Supplementation is not recommended for children, nor should it be used during early pregnancy or to prevent rickets in infants. This is because the safety of vitamin D supplements for these groups has never been tested and their long-term safety is unknown.
Questions about safety have come up regarding its potential effects on bone density and cancer, heart disease, hypertension, multiple sclerosis, as well as an immune response in children.
Vitamin D has been found to reduce the risk of developing prostate cancer by 40% according to a study published in the European Journal of Nutrition in 2011.
It seems to be particularly helpful for those with low levels of vitamin D that have a higher genetic risk factor for developing prostate cancer.
Vitamin D Side Effects
Vitamin D supplements may cause other diseases. Vitamin D toxicity is rare and usually occurs in people who continue to take high doses for a long period of time. Symptoms of vitamin D toxicity include nausea, vomiting, constipation, diarrhea, weakness, and tiredness.
Rarely it may lead to hypercalcemia, which can cause serious problems including kidney stones. Other side effects include low calcium levels and low magnesium levels. Dosage for adults should not exceed 4,000 IU daily unless prescribed by a doctor or healthcare provider due to the risk of toxicity.
Vitamin D is only found in foods of animal origin (e.g., fish liver oil). Vitamin D is not available in plant foods.
Vitamin D is a fat-soluble vitamin that can be stored in the body for later use. For example, a diet deficient in vitamin D will cause decreased uptake of calcium from the intestines, leading to bone softening and weakening. Vitamin D is important in the absorption of calcium.
Vitamin D deficiency is a very serious problem in some areas of the world, such as Africa, Asia, and Australia. Vitamin D deficiency limits the body's ability to absorb calcium and phosphorus efficiently. It also increases the risk of developing osteoporosis, fractures, and chronic diseases such as cardiovascular disease (CVD) and cancer. Vitamin D deficiency can be harmful to individuals who are already at risk for low levels of vitamin D from nutritional or genetic reasons.
Vitamin D Deficiency
Vitamin D deficiency is common in populations with a low intake of foods and animal products that contain vitamin D (e.g., dairy products, eggs, and fish). Oral calcium supplements may also cause vitamin D deficiency if consumed in large amounts over time.
The main function of vitamin D is to support the body's absorption of calcium and phosphorus. Vitamin D deficiency disrupts this process. Since the body stores calcium and phosphorus reserve in the bones, when this reserve is depleted, too much calcium enters the blood, causing injury to soft tissues such as skin or joints. A deficiency of vitamin D can also interfere with the formation of new bone. Vitamin D deficiency impairs the ability to absorb and retain adequate calcium, leading to the following health consequences:
Vitamin D is essential for maintaining strong bones and helping them develop properly during childhood. Without enough dietary vitamin D, young children cannot properly absorb calcium and phosphorus from their diet. This causes weak bones that may result in rickets in children and osteomalacia in adults. It is difficult to get enough vitamin D from foods so many people need supplements or exposure to sunlight.
Vitamin D deficiency is an important cause of osteomalacia, a condition in which bones are soft and may become soft, weak, or fragile. Vitamin D deficiency can also cause delayed bone growth in children and adolescents. Osteomalacia can lead to fractures and decreased bone density that can increase the risk of CVD later in life.
Vitamin D deficiency is also linked to the increased risk of developing multiple sclerosis (MS). Some studies show a correlation between lower vitamin D levels and higher risk for MS, while other studies have shown that vitamin D supplementation prevents MS relapse and enhances the survival of people with MS. Other diseases, such as type-I diabetes, that may be linked to a deficiency of vitamin D include:
Vitamin D and Multiple Sclerosis - Vitamin D deficiency contributes to many chronic diseases such as heart disease and cancer. However, researchers have not been able to prove whether taking vitamin supplements reduces the risk of these illnesses or helps treat them.
It is likely that vitamin D has an influence on health in general. However, at this time it is not possible to give a clear diagnosis on the basis of one ingredient from diet or supplements alone.
There are several factors that can determine if you are likely to develop osteoporosis. Some factors include family history, age, weight, race, and exercise. At this time, it is not possible to make a prediction for individual cases.
Osteoporosis Treatment - If you are prone to osteoporosis or an illness that makes you more susceptible to osteoporosis (e.g., diabetes), your doctor will often recommend taking calcium supplements regularly with vitamin D supplementation. The ideal ratio of calcium to vitamin D is 1:1. However, the average person can absorb only about 30% of the calcium that they ingest through diet and supplements. Therefore, you will take more calcium than necessary if your body absorbs 60% or more of the calcium in your supplements.
Vitamin D is important for the function of the gastrointestinal system. Vitamin D is essential to maintain the integrity of the intestinal tract, particularly in regulating calcium and phosphorus absorption from the intestines.
A study on vitamin D and IBD suggests that higher vitamin D levels are associated with a lower risk of developing Crohn's disease (CD). However, this study also showed that high vitamin D levels did not significantly affect disease duration or severity when compared to people with normal vitamin levels.
There have been several studies on how vitamin D affects diseases like CD (Crohn's disease) and ulcerative colitis (UC). But it is not possible to make a clear correlation between these studies. It is possible that a relationship between vitamin D levels and IBD exists beyond the findings in the studies.
In most cases, the cause of IBD is not known and it is believed that factors are involved in both the development of the disease and its incidence. However, many studies show a correlation between vitamin D and Crohn's Disease.
One major benefit of vitamin D supplementation appears to be to improve calcium absorption in people with chronic diseases preventing them from absorbing enough calcium from their diet. Vitamin D acts as an enhancer of calcium absorption in such people by increasing parathyroid hormone (PTH), which stimulates mineral absorption through several different mechanisms (e.g., increasing gastrin levels, stimulating intestinal contraction, etc.).
Osteoporosis Prevention While osteoporosis is not an autoimmune disease, the risk factors associated with it are similar. For example, studies have shown that vitamin D levels may be lower in women with osteoporosis. According to the National Institutes of Health (NIH): Recent studies have shown a low vitamin D level in postmenopausal women who have low bone mass and/or osteoporosis. In these studies, a low vitamin D level was correlated with increasing calcium loss in the urine. This may increase the risk of developing osteoporosis.